1. Field of Invention
This invention relates to electrical receptacles, and in particular to a protective electrical receptacle having a releasable locking mechanism to secure the plug's terminal prongs within the outlet.
2. Prior Art
A wide variety of electrical receptacles are known to provide electrical connection between male electrical connectors having blade type terminal prongs, commonly referred to as plugs, and female receptacles for receiving the plug's terminal prongs, commonly referred to as outlets.
The most common outlet has a pair of electrical contacts that receive the plug's terminal prongs. The contacts are biased into contact with the prongs, the biasing force of the electrical contacts against the prongs is relatively light and the plug is easily inserted or removed from the outlet. The low withdrawal force creates an inconvenience when an inadvertent tug or twist of the cord will disconnect the plug from the outlet. Continually powered outlets also pose the danger of electrical shock to a curious child who may insert a metallic object such as a key or a bobby pin into the outlet. A user is also posed to the risk of shock upon initial insertion of the plug when the user may unknowingly touch the plug's terminal prongs.
The vast majority of male plugs typically include a small ⅛″ diameter hole within a standard distance from the end of the terminal prong. The prior art includes a variety of examples of how these holes may be engaged to prevent inadvertent release of the male plug, while some designs also add an alternative safety feature to reduce the outlets shocking potential.
In U.S. Pat. No. 5,286,213, the locking action is performed by ramps which urge the outlet's electrical contacts to clamp the broad sides of the plug's terminal prongs, the electrical contacts have small rounded nubs that engage the plugs prong holes. The outlet's contacts are isolated from their power source until the locking action has been performed by the user, which simultaneously energizes the outlet as the electrical contacts are turned into electrical communication with the power source. The principal drawback of this design poses the problem that the outlet is frictionally held in its locked position. An inadvertent twist of the cord can cause the plug to turn within the outlet and reverse the locking step, thus allowing for possible isolation from its power source, and reducing the clamping force applied upon the prongs making inadvertent disconnection more likely. Another drawback seen in this design is that the user must twist the plug relative to the outlet to exert the clamping force upon the prongs. The issue arises when the outlet's turning resistance increases as the ramps apply more clamping force on the electrical contacts to secure the plug's terminal prongs, causing undue stress to the plug's prongs as the user attempts to lock the plug tighter by turning it further. Over time, the extra stress may cause the plugs rigidly fixed prongs to become loose, causing electrical connection issues within the plug and creating a potential fire hazard. Another drawback of the design is that the clamping force must be continuously exerted upon the plug's terminal prongs by the outlet, causing the outlet to be under inherent constant stress anytime it is retaining a plug which may lead to premature wear or breakage to the outlet.
U.S. Pat. No. 5,791,931 has a grasping jaw having a hook portion to engage the plug's prong holes when urged by the moving carrier, which secures the plug's terminal prongs. A safety plug may be inserted and locked within the outlet to block insertion of a metallic object by a child. A key can also be required to unlock the safety plug from the outlet. The locked safety plug does offer an increased level of safety to a curious child by not allowing them to insert a metallic object into the continuously powered outlet, yet offers no increased safety to a user who may unknowingly touch the plug's terminal prongs during insertion. The safety plug or its key, may also easily be misplaced by the user when not in use, making this safety feature less user friendly than a typical outlet.
U.S. Pat. No. 5,795,168 uses a centrally located initiating member to urge locking members with protruding fixed pins to engage the prong holes when the plug is turned within the outlet. Electrical contacts mounted in slots in the outer periphery of the plug receptor grippingly engage fixed energized conductive contacts protruding into the plug receptors cavity to energize the outlet. The main problem seen in this design is that a curious child can still potentially be shocked by inserting a metallic object, such as a bobby pin, into the space between the plug receptors outer periphery and the inner periphery of its cavity to contact the continually powered protruding contacts.
U.S. Pat. No. 7,484,986 B1 uses insulated, manually operated buttons which have a shaft at their inner ends to engage the plug's prong holes. The user presses the buttons inward to engage their shafts through the plug's prong holes to thus secure the plug. This design is not easily adaptable to other arrangements, such as a wall outlet, because the sides of the outlet and the manually operated buttons would not be accessible to the user. This design is also continually energized which poses a risk of shock to an unwitting child who may insert a metallic object into the outlet, or to a user who may unknowingly touch the plug's terminal prongs during insertion.